Color electrophotographic apparatus

ABSTRACT

Color electrophotographic apparatus comprises a plurality of operation stations each of which has a charging section, an optical image exposure section and a developing section. Two sets of endless belts travel between the plurality of operation stations and convey a flexible electrophotographic material. The endless belts contact only the end or edge portions of the electrophotographic material. An optical system is provided wherein the optical axis for exposing the electrophotographic material is maintained in the same position in all the optical image exposure sections, the surface of the photoconductive insulating layer is perpendicular to the optical axis, and the optical images formed on the insulating layer are equal to each other in size during all exposures.

Tamai Dec. 18, 1973 COLOR ELECTROPHOTOGRAPHIC APPARATUS lllll|'llll[|llllllllll Primary Examiner-John M. Horan Attorney-Gerald.1. Ferguson, Jr. et a1.

[ 5 7 ABSTRACT Color electrophotographic apparatus comprises a pluralityof operation stations each of which has a charging section, an opticalimage exposure section and a developing section. Two sets of endlessbelts travel between the plurality of operation stations and convey aflexible electrophotographic material. The endless belts contact onlythe end or edge portions of the electrophotographic material. An opticalsystem is provided wherein the optical axis for exposing theelectrophotographic material is maintained in the same position in allthe optical image exposure sections, the surface of the photoconductiveinsulating layer is perpendicular to theoptical axis, and the opticalimages formed on the insulating layer are equal to each other in sizeduring all exposures.

10 Claims, 3 Drawing Figures PATENTEDnEc 18 I973 3.779.639

SHEET 10E 2 FIG.- I

COLOR ELECTROPHOTOGRAPHIC APPARATUS BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention relates to color electrophotographicapparatus.

2. Description of the Prior Art In one method known in the art ofelectrophotography, a color image is obtained by repeating anelectrophotographic process wherein an electrostatic latent image on aphotoconductive insulating layer is developed using coloring particles(hereinafter referred to as toner).

In order toobtain a color image by the xerox system, it is necessary toobtain a toner image by repeating exposure to an optical imagemaintained in registration with the photoconductive insulating layer anddeveloping the toner images.

This invention is directed to an improved electrophotographic apparatusfor obtaining a color image by the electrofax system. In obtaining acolor image by the electrofax system, it is necessary to carry out atleast the following operations:

The photoconductive insulating layer is subjected to first charging,first exposure (to an optical image of the original passed through agreen color filter, for example), first developing (using amagentatoner), second charging, second exposure (using, e.g., a redcolor filter), second developing (using a cyan toner), third charging,third exposure (using, e.g., a blue color filter), and third developing(using a yellow toner) in the indicated order. These operations areperformed on the same photoconductive insulating layer (photosensitivelayer). Exposure must, of course, be carried out in strict registration.

Because of these troublesome operations, apparatus forelectrophotographically obtaining a color image has hitherto had thedisadvantages of being complex in construction and large in size.Particularly, it has hitherto been necessary to carryout exposure insuch a manner that the photosensitive layer is returned to apredetermined position on the exposure table for registration purposeseach time developing of the latent image in one color is finished. Whenthe photosensitive layer is maintained immovable during the processingoperations, the copying machine used must be such that the chargingdevice and developing device are capable of moving successively acrossthe surface of the photosensitive layer (such as described in U.S. Pat.No. 3,371,651 for example). This problem can be solved by using anoriginal which is separated into its component colors (such as describedin US. Pat. No. 3,307,457). It is, however, time consuming and requiresa lot of manual attention to prepare an original which is separated intoits component colors. Thus, this is not desirable as means for obtaininga duplicate of a color picture for general use.

SUMMARY OF THE INVENTION One object of this invention is to provide anovel color electrophotographic apparatus which obviates theaforementioned disadvantages of convention apparatus.

Another object is to provide a color copier which is simple and involvesno maintenance trouble.

According to the present invention, there is provided anelectrophotographic apparatus in which an electrophotographicphotoreceptor comprising a photoconductive insulating layer provided ona support which is electrically charged and passed at least twicethrough different charging sections and developing sections, and inwhich color separation filters used for different operations of exposureto an optical image have difierent absorption wavelength ranges, and thecolors of the toners in the developing agents used in different operation are complementary to the colors of such filters, characterized inthat the photosensitive surface of the photoreceptor is disposed on andperpendicular to the same optical axis of an optical system for exposingthe photosensitive surface to the optical image in different exposureoperations, optical images formed on the photoreceptor in differentexposure operations are of a substantially identical size, and thephotoreceptor is supported in different positions in theelectrophotographic apparatus during different exposure operations.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical side sectionalview of electrophotographic apparatus according to this invention.

FIG. 2 shows, in a front view and a side view, a roller used in theapparatus according to this invention.

FIG. 3 is a perspective view of essential portions of the apparatusaccording to this invention.

DETAILED DESCRIPTION OF THE INVENTION This invention will now beexplained with reference to the drawings. In FIG. 1, l 1 is aphotoreceptor wound in roll form. The photoreceptor may be wound suchthat the photosensitive layer thereof faces disposed inwardly. In theembodiment shown, however, the photoreceptor is wound such that thephotosensitive layer faces outwardly. The photoreceptor need not bewound in roll form but can be cut into predetermined lengths in sheetform. In the embodiment shown, the photoreceptor 11 is held between apair of rollers 12, 12 and drawn out thereby to be delivered to acutting section comprising a support table 13 and a cutter 14. A lengthof the photoreceptor is cut and conveyed by endless belts 15 and 16while being held therebetween. The endless belts l5 and 16 form a pairand support an end portion of the photosensitive layer. The other endportion of the photosensitive layer is held by another pair of endlessbelts l5 and 16' (shown in FIG. 3 but not shown in FIG. 1). The endportion of a sheet of the photoreceptor cut in a predetermined length bythe cutter 14 is held by the endless belt 15 and 16 at the upper surfaceand underside of a portion designated 17. It is known that in developingan electrophotographic picture without using a liquid developerundesirable background stain (so-called fog) can be obviated by wettingthe photoreceptor beforehand with an insulating liquid containing notoner therein. A highly insulating liquid 19 for obviting backgrounddensity is contained in a vessel 18. Kerosene, mineral spirits,cyclohexane, decaline, isoparaffinic base solvents and silicone oil areknown as liquids which serve this purpose.

The insulating liquid 19 is scooped up by a roller 20 from vessel 18 andtransferred to roller 22 via roller 21. Rollers 20, 21 and 22 are madeof material which may be either hard or soft and either solid or porous.Roller 22 is maintained in contact with the photosensitive layer of thephotoreceptor a length smaller than the distance between the two sets ofendless belts, and applies the insulating liquid to the photosensitivelayer surface to form a coating of the liquid thereon. In thisembodiment, the coating of the liquid is formed prior to charging.However, the coating of the liquid may be formed between charging andexposure to an optical image or between exposure to an optical image anddeveloping.

In this embodiment, the photoreceptor having the coating of the liquidformed thereon is conveyed to a first charging section which comprises acorona electrode 23 and a shield case 24 which is open on one side. Thecorona electrode 23 may consist of either fine metal wires or metalneedless. A high voltage is impressed on the corona electrode 23 from anexternal power source (not shown). When the electrophotographicphotoreceptor contains zinc oxide, a negative the high voltage of 6 KV,for example, is impressed. The surface of the photoreceptor isnegatively charged by the corona discharge from corona electrode 23.

It has been found that it is the surface of the photosensitive layerthat is charged even when the coating of the insulating liquid is formedbeforehand. Charging may be effected by the so-called double coronasystem whereby opposite surfaces of the photoreceptor are charged.

After passing through the charging section, the photoreceptor is passedon to an optical image exposure section. In the drawings, a sheet ofphotoreceptor being exposed to an optical image in the optical imageexposure section is designated 25. Exposure of the photreceptor 25 to anoptical image is not interfered with by the endless belts l and 16 andthe set of endless belts (the endless belts l5 and 16' shown in FIG. 3)

.which only hold the photoreceptor at opposite ends thereof. Theoriginal shown is a transparent positive color picture (color slide) 26.

The original is illuminated by a light source 27. Light rays from thelight source 27 are rendered uniform by a condenser lens 28 and adiffuser 29. 30 designates a set of color separation filters comprisingred, blue and green color filters which are placed in front of or at theback of an image forming lens 31, depending on the steps of theoperation. In the embodiment shown, an optical system comprising thetransparent positive picture 26, light source 27, condenser lens 28,diffuser 29, filters and lens 31 is firmly secured .on a table 32. Thetable 32 is movable for causing an image to be formed on the surface ofthe photoreceptor in each step of exposure of the photoreceptor to anoptical image for each color component.

When the photoreceptor is disposed in the optical image exposure sectiondesignated 10, the table 32 is disposed in the rightmost position inFIG. 1. When the green filter is selected from among the set of filters30 and the photoreceptor is exposed to an optical image through thegreen filter, it is necessary to place the photoreceptor perpendicularto the optical axis in order to prevent distortion of the image formed.Deviation from the perpendicular may be allowed, of course, if thedeviation is negligible. After being exposed to the optical image, thephotoreceptor 25 is conveyed to a developing section. A toner 33 usedfor developing a latent image formed through the green filter asaforementioned is a pigment of magneta color which is dispersed in acarrier liquid.

The developing section comprises a vessel 34 which is divided bypartition plates 35 and 35 into portions for receiving three types ofliquid developer. The partition plates prevent the developer from mixingwith each other. The toner 33 used in the first developing section is ofmagenta color, toner 36 used in the second developing section is of cyancolor and toner 37 used in the third developing section is yellow.Preferably, the colors of the color separation filters and the colors ofthe toners are complementary to each other. However, the filters andtoners available in an actual operation may deviate from thistheoretical ideal. Therefore, the materials used may be as near thetheoretical ideal as possible. A black toner may be used in combinationwith the magenta, cyan and yellow toners. In each developing section,38, 38 and 38" are electrically conducting plates or wire-nettings whichserve as developing electrodes. The photosensitive layer faces outwardlyin the developing sections and is juxtaposed to development electrodes38, 38 and 38". The toners adhere to the surface of the photosensitivelayer by being attracted to or replulsed therefrom by the latent imagesformed by exposure to the optical images.

After the latent image is developed in the first developing section,excess liquid developer wetting the photoreceptor is removed by asqueeze roller 39. The photoreceptor having gone through the primarydeveloping step is conveyed to a second charging portion 40 while beingheld at opposite end portions thereof by the endless belts. The secondcharging station is constructed in the same manner as the first chargingsection. The photoreceptor is conveyed to a second exposure section 41after being charged again. At this time, the table 32 on which theoriginal rests moves leftwardly in the figure, so that an optical imageis formed on the surface of the photosensitive layer in the secondoptical image exposure section 41. In the secondary exposure operation,the red color filter is selected from the filters 30 and moved to aposition in which it is disposed in front of the image forming lens inthis embodiment. A latent image formed by exposing the photosensitivelayer to the optical image is developed using cyan color toner 36.Following developing, the photoreceptor is squeezed by a squeeze roller39'.

After going through the second developing step, the photoreceptor thenpasses through a third charging section 42 to be conveyed to a thirdoptical image exposure section 43 where a blue color filter is selectedfrom among the set of filters 30.

The moving distance of the table 32 leftwardly in the figure is equal tothe distance between the first optical -image exposure section 10 andthe second optical image exposure section 41.

After going through a third developing step, the photoreceptor which hasbeen squeezed by a squeeze roller 39" is conveyed to a drying section 44where it is exposed to an air current from a fan 45. The air current isindicated by the arrow. In the drying section 44, the carrier liquidwetting the photoreceptor is removed.

The photoreceptor formed thereon with a color toner image afterdeveloping of the latent images in three colors is finished is strippedfrom the endless belt 16 by a guide plate 46 and placed on a plate 47.

In the apparatus shown in FIG. 1, rollers 48, 48' and 48" disposed inthe respective charging sections are preferably electrically conductingand electrically grounded so as to provide an uniform charge.Preferably, the rollers 48, 48' and 48" and rollers 49, 49 and 49" ofthe respective developing sections have end portions 50 which arenarrowed an amount corresponding to the width 51 of the endless belts asshown in FIG. 2. Its depth 52 is equal to the thickness of the endlessbelt 15. 53 and 53' are shafts. It is required that the three squeezerollers 39, 39' and 39" be narrowed similarly at their end portions orslightly shorter than the distance between the two sets of endlessbelts.

FIG. 3 shows the first charging section and first optical image exposuresection 32 and a portion of the optical system. All reference numeralsare corresponding to those ofFIG. l. The photoreceptor 25 has passedthrough the first charging section where it has been negatively chargedby being subjected to a corona discharge from the corona electrodeassembly 23, 24 on which a high voltage is impressed, before beingdisposed in the position shown in the figure. The photoreceptor is heldat opposite end portions thereof by the two sets of endless belts 15, 16and 16'. An'image of the transparent positive original 26 disposed onthe right in the figure is formed on the photosensitive layer 25 by theimage forming less 31, so that an electrostatic latent imagecorresponding to the original is formed on the surface of thephotosensitive layer 25.

Although lacking in the apparatus described above, a device may beprovided for carrying out the opera tion of washing the surface of thephotoreceptor with a highly insulating liquid containing no toner afterthe photoreceptor has passed through various developing sections. Theprovision of this device is conductive to increasing the quality of thecolor image obtained in which background density is minimized. The sametype of carrier may be used within the different colors developer; theuse of a carrier liquid of particularly high volatility facilitatesdrying. The colors of the toners of the developer should becomplementary with the colors of the color separation filters.Therefore, developing of the image in different colors may be carriedout in any color's desired, so long as the colors of the toners are in apredetermined relation with the colors of the filters.

In the embodiment described above, the table 32 on which the originaland optical system rest moves along the same optical axis whenever theoptical image exposure operation is carried out in different colors.Alternatively, the lens along may have its position and focal lengthvaried without moving the light source, con denser lens, diffuser andoriginal as indicated in FIG. 3 at 65. Even in this case, the opticalaxis must remain in the same position and the images formed must besubstantially equal in size. A zoom lens of any type as desired which iscommercially available can be used to attain the end.

In the apparatus according to this invention, duplicates of colorprinted matter or a color print may be made by using a reflectionexposure system. The use of an image forming lensand a reflector isessential when the reflection exposure system is employed. Even in thiscase, liquid images formed on the photoreceptor must register with oneanother and be substantially equal in size in the optical image exposureoperation in different colors. Exposure to an optical image may be inthe form of either stationary exposure or scanning exposure. Intransmission exposure and reflection exposure, different lenses may beused for the optical image exposure and operations in different colors.This process and the use of zoom lens best facilitate registration ofimages. In effecting registration, a microswitch or photocell ispreferably used for detecting the movement of the photoreceptorsupported by the endless belts. The position in which the photoreceptoris held must be kept constant with respect to the optical axis at alltimes.

A method for enforcing an exact registration is described in FIG. 3. Inshort, 60 and 61 are units of lightsource, whose inward provide alight-source, a lens and a pin-hole like slit, and therein emit a minutelight beam toward the direction of the arrow as shown in the drawing. Onthe other hand, 62 and 63 are photo-cells which receive light from theunits of light source. The apparatus is provided with means to stop theendless belts when electrical resistance becomes identical in the twophoto cells or a light electromotive force.

This stopping function occurs after leading edge of the photosensitivepaper 25 passes said unit 60 and photo cell 62. The distance betweensaid unit 60 and unit 61 (or photo cell 62 and photo cell 63) is decidedto be as long as the photosensitive cut paper 25 or less longer.

When the photosensitive paper 25 is sent by the endless belt of thisapparatus, and the leading edge and trailing edge of the paper passesjust, both elements 62 and 63 are equivalent in electric resistance orlight electromotive force and the proceeding of a paper 25 is stopped.

Then the registration is performed as a photosensitive paper is inaveyance on a settled position.

In FIG. 1, if said units of light source and said photocells areprovided respectively on the right of the first optical image exposuresection 10 and on the left of the third optical image exposure section43, the registrations at the optical image exposure sections of thefirst, the second and the third can be completely performed.

Of course, said two light beams should be made to transit a portion nearthe endless belt, i.e., a portion near the side end of thephotosensitive paper, since it is undesirable that the light beamsproject to the surface of the photosensitive paper charged electrically.

One of the features of the apparatus according to the present inventionis that no malfunction occurs in moving the photoreceptor because thephotoreceptor is coveyed while held by two sets (four in number) ofendless belts at all times.

Developing is not confined to liquid developing in the apparatusaccording to this invention. That is, a cascade developing process,powder cloud developing process, magnetic brush developing process andsimilar processes may also be used.

The liquid developing process is particulary superior to other processesin faithfully reproducing tonal gradients. In the apparatus according tothis invention, when the charge of the electrostatic latent image andthe charge of the toner have different signs, negative to positive workis carried out, e.g., to obtain a color print from a negative colorpicture. In this case, a bias voltage is impressed on developingelectrodes 38, 38 and 38". These electrodes are grounded when positiveto positive work is being carried out. By using the appara tus accordingto this invention, it is possible to obtain a color picture image ofhigh quality quite readily. Maintenance of the apparatus can beperformed readily, and no jamming of the photoreceptor occurs in theapparatus.

What is claimed is:

l. A color electrophotographic apparatus comprising conveying means forsequentially conveying a sheet of electrophotographic material to atleast two exposure sections disposed a predetermined distance apart;

means for charging said electrophotographic sheet prior to it beingconveyed to each said exposure section;

means for sequentially image exposing said electrophotographic materialat each of said exposure sections, said image exposing means having anoptical axis along which said two exposure sections are disposed andincluding means for making the optical images on the surface of theelectrophotographic sheet equal to one another in size at each of theexposure sections to accommodate said predetermined distancetherebetween; and

means for developing the latent images on said electrophotographic sheetresulting from the image exposures at said exposure, said developingoccuring after each said exposure section,

said sheet being conveyed by said conveying means across said opticalaxis in a first direction at the first of said two exposure sections andin a second direction across said optical axis at the second of said twoexposure sections.

2. Apparatus as in claim 1 where said means for making the opticalimages equal to one another includes means for moving said exposuremeans said predetermined distance between each of said sequentialexposures.

3. Apparatus as in claim 1 where said conveying means comprises twopairs of endless belts where one pair grips one side of said sheet andthe other pair grips the other side, at least a portion of said endlessbelts traversing a path which respectively perpendicularly crosses theoptical axis of said exposure means at said exposure sections.

4. Apparatus as in claim 3 including means for moving said two pairs ofendless belts at the same speed.

5. Apparatus as in claim 3 where each said pair of endless belts areseparated at a point subsequent to the last developing means to permitthe removal of the developed electrophotographic sheet therefrom.

6. Apparatus as in claim 1 where said exposing means includes aplurality of filters of differing colors, a different filter beingintroduced for each exposure for color separation.

7. Apparatus as in claim 6 where said developing means includes meansfor developing said latent images with colored toners, the colors ofwhich are respectively complementary to said color separation filters.

8. Apparatus as in claim 7 where said toners are magenta, cyan, andyellow respectively.

9. Apparatus as in claim 1 where said first direction is opposite tosaid second direction.

10. Apparatus as in claim 1 where said conveying means includes meansfor gripping said sheet at each side thereof.

1. A color electrophotographic apparatus comprising conveying means forsequentially conveying a sheet of electrophotographic material to atleast two exposure sections disposed a predetermined distance apart;means for charging said electrophotographic sheet prior to it beingconveyed to each said exposure section; means for sequentially imageexposing said electrophotographic material at each of said exposuresections, said image exposing means having an optical axis along whichsaid two exposure sections are disposed and including means for makingthe optical images on the surface of the electrophotographic sheet equalto one another in size at each of the exposure sections to accommodatesaid predetermined distance therebetween; and means for developing thelatent images on said electrophotographic sheet resulting from the imageexposures at said exposure, said developing occuring after each saidexposure section, said sheet being conveyed by said conveying meansacross said optical axis in a first direction at the first of said twoexposure sections and in a second direction across said optical axis atthe second of said two exposure sections.
 2. Apparatus as in claim 1where said means for making the optical images equal to one anotherincludes means for moving said exposure means said predetermineddistance between each of said sequential exposures.
 3. Apparatus as inclaim 1 where said conveying means comprises two pairs of endless beltswhere one pair grips one side of said sheet and the other pair grips theother side, at least a portion of said endless belts traversing a pathwhich respectively perpendicularly crosses the optical axis of saidexposure means at said exposure sections.
 4. Apparatus as in claim 3including means for moving said two pairs of endless belts at the samespeed.
 5. Apparatus as in claim 3 where each said pair of endless beltsare separated at a point subsequent to the last developing means topermit the removal of the developed electrophotographic sheet therefrom.6. Apparatus as in claim 1 where said exposing means includes aplurality of filters of differing colors, a different filter beingintroduced for each exposure for color separation.
 7. Apparatus as inclaim 6 where said developing means includes means for developing saidlatent images with colored toners, the colors of which are respectivelycomplementary to said color separation filters.
 8. Apparatus as in claim7 where said toners are magenta, cyan, and yellow respectively. 9.Apparatus as in claim 1 where said first direction is opposite to saidsecond direction.
 10. Apparatus as in claim 1 where said conveying meansincludes means for gripping said sheet at each side thereof.